The present invention relates to a device designed to recover the forces generated by an aircraft engine, in order to retransmit them to a structure of the aircraft, such as a wing or fuselage element, by means of an engine strut.
More precisely, the invention relates to a device intended to recover the engine couple together with the forces produced by the engine along lateral and vertical directions relative to a longitudinal axis of the engine.
Engines equipping aircraft are suspended under the wing or attached laterally onto the fuselage by means of an engine strut.
The connection between the engine and the engine strut is ensured by systems generally constituted of two or three supplementary attachment devices, each fulfilling a certain function.
Documents U.S. Pat. No. 5,620,154, U.S. Pat. No. 5,275,357 and U.S. Pat. No. 6,059,227 describe the different attachment devices existing at present. Each of these devices comprises a principle attachment structure and an emergency attachment structure. The principal attachment structure ensures transmission of forces during normal operation, that is when all the parts of the attachment device are intact. The emergency attachment structure is provided to ensure continuity of the function of transmission of effort between the engine and the aircraft in the event of rupture of one of the parts of the principle attachment structure.
The existing attachment devices, such as those shown in the documents named above, usually comprise an intermediate fitting, fixed to the engine strut, for example by means of screws, and at least two ball pivoted rods, ensuring the connection between the fitting and the engine. The ball pivot mounting of the rods on the fitting and on the engine makes it possible to prevent the structure continuing forces along the longitudinal axis of the engine.
Existing attachment devices are fixed on the one hand to the engine and on the other hand to the engine strut. The latter constitutes the connection interface between the propulsive assembly, constituted by the engine and the pod surrounding it, and the structure of the aircraft, constituted by the wings or the fuselage.
More precisely, the engine strut enables the forces generated by the engine to be transmitted to the plane. It also ensures the supply of fuel, electricity, hydraulics and air between the engine and the aircraft. Furthermore, it has to withstand various stresses such as aerodynamic drag, minimum mass and cost for maximum safety.
Usually, an engine strut comprises two sub-assemblies formed by a primary structure and a secondary structure, together with equipment.
The primary structure of the engine strut is constituted of a framework and lateral panels. It ensures the transmission of the forces exerted by the engine to the structure of the aircraft. For this reason, its rigidity must be high.
The secondary structure of the engine strut comprises all metallic shell elements added to the primary structure. These elements fulfil different functions such as aerodynamic functions (in order to limit the drag due to the engine strut), protection functions and separation functions for the systems crossing the engine strut, functions of accessibility to the primary structure elements etc.
On modern planes, the primary structure of the engine strut is of the xe2x80x9cboxxe2x80x9d type. It comprises a lower spar, an upper front spar, an upper rear spar, ribs for connecting said spars and lateral panels enclosing the engine strut. In certain cases, an intermediate fitting is set between the attachment device of the engine and the engine strut. It is generally fixed on one of the fittings by four bolts.
In this known arrangement, the forces generated by the engine are transmitted from the intermediate fitting to the strut box and then to the wing or the fuselage through the four bolts, the rib and the lateral panels of the engine strut. The rib fulfils the function of stabilising the lateral panels stressed in traction and compression.
When using an engine generating greater forces than existing planes, such as an engine with a greater weight and level of propulsive thrust relative to existing engines, all the active elements of the attachment device of the engine and the, engine strut must be able to recover these forces and transmit them to the wing or to the fuselage.
In order to take up the forces generated by the increase in mass and the level of propulsive thrust of new engines, it is necessary to increase the number of fixations between the strut and the attachment device of the engine. The number of fixations can be doubled, for example. Resulting from this increase, one can increase the size of the fitting receiving these fixations and make it more rigid.,
This can then lead to increasing the dimensions of the rib of the engine strut through which the forces are usually transmitted to the wing or the fuselage, to take into account the change in dimensions of the intermediate fitting and the increase in the thrusts to be recovered.
However, the large dimensions then required of the rib could lead to serious problems. The machining of a part of such large dimensions is difficult and very long since machining has to take place in the mass. Furthermore, such a part is heavy, bulky and costly. In addition, it is difficult to mount. Finally, the forces. transit the whole of the fitting and thus do not have any privileged path. This requires using a totally rigid fitting, to avoid problems of cracks and breaks, which increases the mass even further.
The precise aim of the invention is a device for recovering forces generated by an aircraft engine, with an original design making it possible to simplify its machining and mounting, and to limit its weight, its bulk and its cost, when the size of the engine leads to an increase in the dimensions of the intermediate fitting.
According to the invention, this result is obtained by means of a device for recovering the forces generated by an aircraft engine, comprising an engine strut able to be fixed to a structure of the aircraft and at least one attachment device fixed to the engine strut and capable of supporting the engine, the attachment device comprising an intermediate fitting fixed to the strut by first fixation means, characterised in that the engine strut comprises, facing the attachment device, several strut fittings independent from each other, the intermediate fitting being fixed to each of the strut fittings by the first fixation means.
This arrangement makes it possible to transmit the forces through symmetrical strut fittings of small dimensions, whose machining is simple and rapid. Furthermore, these independent strut fittings are lighter and thus easier to manipulate and mount on the strut.
The independence of the strut fittings makes it possible to channel the path of the forces from the attachment device to the wing or the fuselage, in a single principal direction. Thus a better division of forces is ensured. Each of the strut fittings is thus stressed in a balanced way, avoiding detrimental structural fatigue.
In the usual way, the engine strut generally comprises a lower spar as well. The first fixation means then advantageously comprise bolts connecting the intermediate fitting to the strut fittings through the lower spar.
Usually, the engine strut generally comprises two lateral panels as well. Preferably, these panels are then fixed respectively on the independent strut fittings by the second fixation means.
In a preferred embodiment of the invention, the intermediate fitting is fixed to two pairs of independent strut fittings by the first means of fixation.
Advantageously, in this preferred embodiment of the invention, the engine strut also comprises a rigidifying rib, placed between the two pairs of. independent strut fittings and fixed to the latter by the third means of fixation.